Flight simulators conventionally employ wide-angle panoramic collimated projection displays that provide high-fidelity seamless imagery for cross-cockpit/cab viewing. FIG. 1 illustrates such a conventional cross-cockpit flight simulator consisting of simulator cockpit 20 and a cross-cockpit flight-simulation display system formed with a group of video projectors 22, spherically curved back-projection screen 24, and spherically curved collimating mirror 26. Projectors 22 project video images onto the back of screen 24. The video images pass through back-projection screen 24 and appear on its front surface. Collimating mirror 26 reflectively collimates the scattered image light coming from the front of screen 24 to produce a composite virtual image of the images projected by projectors 22. In particular, rays of the light reflected by collimating mirror 26 after being scattered from any point on the front of screen 24 travel largely parallel to one another and are thus collimated. The virtual image produced by collimating mirror 26 is viewable at cockpit 20. At least three projectors 22 are normally needed to achieve the commonly desired viewing angles of 180°-220° horizontally and 40°-60° vertically at cockpit 20.
For the purpose of better understanding the projection optics, FIG. 2 presents a side view of the conventional flight simulator of FIG. 1 as taken along a vertical plane through the projection axis of one of projectors 22. This projector 22 is referred to here as illustrated projector 22. Item 28 in cockpit 20 indicates a viewer, specifically one of the viewer's eyes.
Illustrated projector 22 and spherically curved screen 24 are arranged so that light rays 30 of the image projected by illustrated projector 22 impinge on the concave back surface of screen 24. A group of light rays 30 distributed across the exit aperture of illustrated projector 22 impinge on each different point on the back of screen 24. FIG. 2 illustrates only one light ray 30 in each such group of rays 30. Part of the light formed by light rays 30 passes through screen 24 and is scattered forward (in various directions). Some of the forward-scattered light reflects off the concave surface of collimating mirror 26 and reaches viewer 28. Items 32 in FIG. 2 indicate rays of this forward scattered light. Items 34 in FIG. 2 indicate the reflected light rays that reach viewer 28.
Items 36 in FIG. 2 indicate central axes of the groups of light rays 30 impinging on different points on the back of spherically curved screen 24. Although central axes 36 are illustrated as being largely perpendicular to respective planes locally tangent to screen 24 in the conventional flight-simulation display system depicted in FIG. 2, this is generally not required in projector-based prior art flight simulators. In any event, the maximum intensity of the forward-scattered light generally occurs along central axes 36. In order for viewer 28 to receive reflected light rays 34, collimating mirror 26 is tilted relative to screen 24. As a result, scattered light rays 32 do not travel along central axes 36. The intensity of the light provided by off-axis scattered light rays 32 is less than the intensity of the forward-scattered light traveling along central axes 36. The intensity of the reflected light reaching viewer 28 is reduced, thereby causing the light-processing efficiency of the conventional projector-based flight-simulation display system of FIGS. 1 and 2 to be reduced.
Additionally, the tilting of collimating mirror 26 to screen 24 commonly produces severe image distortion and astigmatism. The noise level of the blend zones is twice as much as the surrounding area. This significantly reduces the contrast and can cause poor image uniformity across the full field of view. In short, the image intensity and image quality of the conventional flight-simulation display system of FIGS. 1 and 2 are often undesirably low.
Furthermore, the geometric complexity of projector-based flight-simulation display systems such as that of FIGS. 1 and 2 commonly causes setup, maintenance and monitoring costs to be very high. Performing image blending between adjacent channels across the projector overlap regions for reducing mismatch of brightness, contrast and color is invariably laborious and time consuming. The cost of replacing light sources in projector-based flight-simulation display systems is considerable due to short lifetimes of light sources currently used in these projector-based systems.
It would be desirable to have a flight-simulation display system having higher light-processing efficiency, as well as greater image intensity and better image quality, than conventional projector-based flight-simulation display systems such as that of FIGS. 1 and 2. It would also be desirable to avoid the various difficulties arising from use of multiple projectors. In addition, it would be desirable for the flight-simulation display system to take advantage of advances in light-source technology, especially in light-emitting diodes.